Silver alloy and method of making same



Patented 1 8, 1927.

UNITED STATES 1,614,752 PATENT OFF-ICE.

WALTER L. MITCHELL, OF NEWARK, NEW JERSEY, ASSIGNOR TO TIFFANY & OOH- PANY,'OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

SILVER ALLOY AND METHOD OF MAKING No Drawing.

My invention relates to improvements in silver alloys and the method of producing the same. The object of my invention is to produce a silver alloy which will not readily tarnish, and which is of such a nature that any apparent deposition on the surface can be easily removed so as to leave the body of the metal clean and bright. Another object of my invention is to produce. a silver alloy which can be worked as readily as the ordinary commercial silver used in manufacturing silver articles, which will have the characteristics above noted, and which will comply with the requirements for sterling silver marking, to wit, that the alloy shall be 925/1000 silver.' In obtaining the above result I use as an important element ofthe alloy an alkali metal, preferably sodium, although other alkali metals such as potassium may be used with fairly satisfactory results. It has also been found that certain of the alkali earth metals such as calcium can be used in place of an alkali metal such as sodium. So far, however, I have had the best results with sodium. v

To effect the combination of the alloyed metal I have found the following method most satisfactory. First to make a' sodium silver alloy rich in sodium, preferably about 10% sodium. I then make a silver zinc alloy containing about 95% silver and 5% zinc, and while the latter is in a molten condition, some of the silver sodium alloy is immersed in the silver zinc alloy and absorbed y 1t. I v

The proportion of the added alloy is regulated by additions of zinc so that the final product will analyze approximately 93% silver, 6 zinc,.and to of one per cent sodium. This meets the requirement of the sterling silver markings. The above mentioned {roportions of the several elements have been found to result in a satisfactory article but obviously the propor-- tions of the elements may vary within certain limits and it has been found in practice that while to of one percent sodium or other alkali metal results in a highly satisfactory article yet sodium to the extent of from of one percent to two percent can be used. Alloys containing higher percentages of alkali metal can be made, but are not workable and are very unstable in the atmosphere.

As compared with the ordinary sterling practically at once, and the white oxide pro- Applieation filed August 14, 1924. Serial No. 732,118.

silver (silver copper), the sodium alloy is slightly softer, and if for domestic or other --uses harder silver is desired, a small portion of tin antimony or some other hardening agent may be added.

The samples which I have tested of the above alloy showthe accumulation of dirt due to condensation of moisture particles in 'the air carrying the dirt, but when these particles are cleaned off, the surface appears bright and untarnished even after a considerable time of exposure.

Apparently the atmosphere acting on the surface of the metal produces an alkaline oxide of sodium, or potassium, as the case may be, which protects the silver from the action of the compounds of sulphur that occur in the atmosphere, that is the oxidation of the sodium or other mineral takes placetects the silver from the formation of the black sulphide, which is the most common tarnish of silver.

My'invention, however, is not'limited to this theory, but the fact remains that the alkali metal alloy does have the effect of protectingthe silver from serious discolora- A 'tion, and that the slightapparent tarmsh that may occur can be readily removed, leaving the silver bright. I have found, however, that the alkali metal such as sodi-' um is not effective when combined with the ordinary silver copper alloy. I

I claim 1. A tarnish resisting silver alloy containing over 90% silver and an alkall metal in amount suflicient to produce an alloy softer than the usual commercial silver alloy and the formation of an easily removable deposit when exposed to the atmosphere.

2. A tarnish resisting silver zinc alloy containing over 90% silver, approximately 5% zinc and an alkali metal in amount sufli- .cient to produce an alloy softer than the usual commercial silver alloy and the for- 100 mation of an easily removable deposit when exposed to the atmosphere.

3. A silver zinc alloy containing over-90% silver, approximately 5% zinc and approximately 2% alkali metal, said. alloy being 105 characterized by being softer than the usual commercial silver alloy, and when exposed to the atmosphere it. accumulates an easily removable deposit.- 1

4. A silver zinc alloy suitable for sterling U silverware and meeting the sterling silver requirement ,for silver content, containing of 1% to 2% of an alkah metal and a hardening agent and characterized by the a fact that when exposed to the atmosphere it accumulates an easily removable deposit which leaves the metal bright after removal.

5. A silver alloy containing over 90% silver and sodium in amount sufficient to produce an alloy softer than the usual commercial silver alloy.

6. A silver zinc alloy containing over 90% silver,'a hardening agent, and sodium of an amount suflicient to produce an alloy softer than the usualcommercial silver alloy and the formation of an easily removable deposit when exposed to the atmosphere.

7. Sterling silver including over 90 percent of silver and of 1% to two percent of an alkali metal.

8. Sterling silver comprising an alloy of over 90 percent silver, five percent zinc and of 1% to two percent of an alkali metal. 9. Sterling silver comprising an alloy of over 90 percent silver, five percent zinc and of 1% to two percent of sodium.

10. The herein described method of makalloy is molten, absorbing some of the first alloy by the second.

12; 'ljhe herein described method of make mg a silver alloy, which consists in troducing a silveralkali metal alloy into a molten I mass of silver zinc alloy.

13. Theherein described method of producing a silver alloy which consists in introducing a silver sodium alloy into a mass of molten silver zinc alloy, whereby the first mentioned alloy is combined with the second.

In testimony whereof, I have signed my nameto this specification this twelfth day of August, 1924.

WALTER L. MITCHELL. 

